In recent years, a so-called lithium ion secondary battery that uses a carbon material such as graphite in a negative electrode and a lithium-containing metal oxide such as LiCoO2 in a positive electrode, being high in the capacitance, as a potential electric storage device, is put into practical use as a main power supply mainly of a note book computer or a portable telephone. The lithium ion secondary battery is a so-called rocking chair type battery where, after assembling of the battery, a charge operation is carried out to supply a lithium ion from the lithium-containing metal oxide as the positive electrode to the negative electrode, and, in a discharge operation, the lithium ion at the negative electrode is returned to the positive electrode. The lithium ion secondary battery is characterized by having a high voltage and a high capacitance.
On the other hand, under a situation where the environmental problems come to the front, an electric storage device (a main power supply and an auxiliary power supply) for an electric car or hybrid car that substitutes for a gasoline vehicle has been actively developed. Furthermore, until recently, as an automobile electric storage device, a lead battery has been used. However, since electrical installations and instruments are fulfilling, from viewpoints of the energy density and output density, a new electric storage device is in demand.
As such a new electric storage device, the lithium ion secondary battery and an electric double layer capacitor are gathering attention. However, the lithium ion secondary battery, though high in the energy density, has problems with the output characteristics, the safety and the cycle lifetime. On the other hand, the electric double layer capacitor, which is utilized as a power supply for back-upping a memory such as an IC and LSI, is smaller in the discharge capacity per one charge than a battery. However, the electric double layer capacitor is provided with such high output characteristics and maintenance-free characteristics that are not found in the lithium ion secondary battery as that the instantaneous charge and discharge characteristics are excellent and several tens thousands cycles of charge and discharge can be withstood.
Although the electric double layer capacitor has such advantages, the energy density of an existing general electric double layer capacitor is substantially 3 to 4 Wh/l and is smaller by substantially two digits compared with that of the lithium ion secondary battery. When an electric car is considered, it is said that, in order to put into practical use, the energy density of 6 to 10 Wh/l is necessary, and, in order to popularize, the energy density of 20 Wh/l is necessary.
As an electric storage device that responds to such applications that necessitate the high energy density and high output characteristics, recently, an electric storage device called as well as a hybrid capacitor that combines electric storage principles of a lithium ion secondary battery and an electric double layer capacitor is gathering attention. The hybrid capacitor usually uses a polarizable electrode in a positive electrode and a non-polarizable electrode in a negative electrode and is gathering attention as an electric storage device that combines high energy density of a battery and high output characteristics of an electric double layer. On the other hand, in the capacitor, a capacitor is proposed in which a negative electrode that can store and release a lithium ion is brought into contact with metal lithium to allow storing and carrying (hereinafter, in some cases, referred to as doping) the lithium ion chemically or electrochemically in advance to lower a negative electrode potential, and, thereby, it is intended that the withstand voltage is heightened and the energy density is made remarkably larger (Patent literatures Nos. 1 through 4).
In the capacitor, though high performance can be expected, when a lithium ion is doped to a negative electrode, metal lithium has to be stuck to an entire negative electrode or it is possible to locally and partially dispose metal lithium in a cell to bring into contact with a negative electrode. However, there are problems in that the doping takes a very long time and cannot be uniformly applied over an entire negative electrode. It is considered difficult to put into practical use in a large and high capacity cell such as, in particular, a cylindrical device where electrodes are wound or a rectangular battery where a plurality of sheets of electrodes is laminated.
However, the problems were overcome at one stroke owing to an invention in that when a hole that penetrates through front and back of a negative electrode current collector and a positive electrode current collector that constitute a cell is disposed to allow a lithium ion moving through the throughhole and simultaneously the metal lithium that is a supply source of the lithium ion and the negative electrode are short-circuited, only by disposing the metal lithium at an end of the cell, the lithium ion can be doped over an entire negative electrode in the cell (Patent literature 5). The lithium ion is usually doped to the negative electrode. However, it is disclosed in the patent literature 5 that even when the lithium ion is doped to the positive electrode together with the negative electrode or in place of the negative electrode, a situation is same.
Thus, even in a large and high capacity cell such as a cylindrical electric storage device where electrodes are wound or a rectangular electric storage device where a plurality of sheets of electrodes is laminated, to an entire negative electrode in the device, in short time and uniformly over an entire negative electrode, the lithium ion can be doped to improve the withstand voltage and thereby to drastically increase the energy density. As the result, a prospect of realizing a capacitor that has high output density that the electric double layer capacitor intrinsically has and high capacitance is obtained.
However, in order to put such high capacitance capacitors into practical use, together with higher withstand voltage, higher capacitance, higher energy density and lower internal resistance, the long term sustainability of the characteristics are further in demand.    [Patent literature 1] JP-A-08-107048    [Patent literature 2] JP-A-09-055342    [Patent literature 3] JP-A-09-232190    [Patent literature 4] JP-A-11-297578    [Patent literature 5] WO98/033227
The invention intends to provide, in a lithium ion capacitor where a positive electrode active material is a material that can reversibly carry a lithium ion and/or anion, a negative electrode active material is a material that can reversibly carry a lithium ion, and a negative electrode and/or a positive electrode is brought into contact electrochemically with a lithium ion supply source to dope the lithium ion in the negative electrode in advance, a lithium ion capacitor that has, together with higher withstand voltage, higher capacitance, higher energy density and lower internal resistance, excellent endurance of sustaining the characteristics over a long term.